I have successfully installed a resin.io image on my pi3. Now I can’t boot the PI with a normal Rasbian image anymore. I realized that I do not need Resin.io and I just want to get back to normal again. The problem is that the pi doesn’t boot anymore with a normal rasbian image and it seems that I can’t flash any other images except for the resin.io images.
I have already delete the device but it did not help.

Can somebody point out to a step-by-step instruction how I can restore to factory settings?